1. Field of the Invention
The present invention relates to the field of highly available database clusters. More specifically, the invention relates to database clusters that transparently move client connections between hosts.
2. Description of the Related Art
A database is generally considered to be a collection of information or data organized in a way that computer programs can quickly access or select desired portions of the collection. A database management system (DBMS) includes the collection of computer programs that enable the quick storage, selection, modification, and extraction of desired portions of data from the database. Exemplary DBMSs include those commercially available from Oracle Corporation, IBM, or the like. Application programs, on the other hand, typically include client programs that connect to a DBMS to provide users the ability to interact with the data of the database, such as, for example, to select, modify, organize, delete, or the like, some or all of the foregoing data. Exemplary application programs include payroll or inventory programs, online stores, or the like.
Often, the application programs are designed to be continually connected to a DBMS, thereby having substantially continuous access to data stored within the same. Unless specifically coded to recover, these application programs typically fail when their connection to the DBMS fails or is otherwise unavailable, such as during a system failure. For many application program environments, this failure is undesirable.
System designers have created various solutions to reduce the effects of an application program losing a connection to a DBMS. For example, system designers often employ database clusters to offer backup solutions to failed systems. Database clusters can include two or more DBMSs accessing shared data files. For example, the shared data files can include data files having the same set of data from the replication of changes from one DBMS to another. Also, the shared data files can include multiple DBMSs that access the same physical storage. Through the shared data files, system designers allow one DBMS to replace another in the event of a failure.
There are several drawbacks associated with the foregoing database clustering solution, especially when employed in environments allowing for little or no down time, such as, for example, high availability solutions. For example, when a DBMS fails, the connection from the application program to the DBMS can be lost, thereby potentially losing all open transactions from the same. Additionally, data not replicated from a failing DBMS can be lost. Moreover, during load balancing, simultaneous updates of the same data on different DBMSs can occur in some replication solutions. Also, a large amount of communication traffic among a cluster, and/or hardware limitations of the same, can reduce the cost effectiveness of geographically diverse systems. Moreover, as discussed, the failure of an individual DBMS results in a failure of non-fault tolerant program applications.
On the other hand, system designers may also employ application servers in order to reduce the effects of losing a connection to a DBMS. For example, system designers often have application programs connect to an application server, where the application server includes the functionality to recover lost client connections to one or more secondary DBMSs within a database cluster. However, the application server generally includes a proprietary protocol used in communications from the application program to the application server. The proprietary protocol is generally not native to the DBMS and therefore, each connecting application program will first be routed through the application server. Thus, the application server solution is not well suited for geographically diverse storage systems.
Embodiments of the present invention seek to overcome some or all of these and other problems.